Testing greaseproof paper



Oct. 6', 1942. M. G. SCHMITTVET AL 2,297,990

TESTING GREASEPROOF PAPER Filed Jan. 14, 1942 /-O|L STAIN Patented Oct. .6 1942 UNITED STATES PATENT OFFICE 1 v 'rns'rmc elflfisi iloor PAPEB' Milton G. Schmitt, Kaukauna, and Martin L.

- 5 I .co'nsin ,7 Downs, Appleton, Wis, asslgnors' to Thilmany Pulp & Paper Company, a corporation of Wis-1 Application January 14, 1942, Serial No. 426,710 ('01. 73-51) '2 3Claims.

Our invention relates to the testing .of the ability of paper. to resist penetration by grease or ,oil,.-and particularly relates to the testing of evaluation of papers of the character which are sold under the general design'ationof greaseproof paper's,jfor example certain types of glassine or otherpapers which are employed in the wrapping or packaging of various food and other products which contain oleaginous-ingredients., v

The primary object ofthe invention is to provide a method of evaluating the greaseproof charin general to'prov'ide an efiicient method of the. character referred to,

General method In order to evaluatethe greaseproof properties of various kinds and weights'of paper, we have found it to be inaccurate,unreliable and imprac- 4 greaseproof properties of which in actual practice have been determined. Hence, according to our preferred practice, as a preliminary step to the practicing of our improved method, we select samples from various types of paper which have 'difierent but known greaseproof properties when used commercially for packing food stuiis or for other purposes. A sufficient selection is made in order to provide samples of paper having the very highest greaseproof properties and those papers which have lower and still lower greaseproof properties until finally, at the bottom .of

by which to' compare or evaluate the greaseproof properties of. a sample of paper .to be tested. A sample ofsuch paper to be tested is then subjected toa similar procedure, and the visual appearance of said sample, after. having been subjected to said procedure, is compared with the visual appearance of the" set of standard'samples which have previously been prepared.

In. order to make these standards permanent and readily available for anyone to use in testing has been no available procedure by, which thegeneral scheme above outlined could be practiced. Therefore, the principal problem has been -to evolve a practical method or treatment to which the standard samples and the test samples could be subjected so as to give uniformly reliable results. All reasonable requirements aresatisfied by the method of treatment which we [will now describe. E

A section of paper of suitable size, for example four inchesby four inches, is coated on one side only with a pigment, preferably in such a manner that the only addition to the paper consists in the pigment coatingwhich has been applied.

Preferably the pigment is of such character that the coating, when dry, will be in the form of a coherent continuous film of such thickness as to be quite opaque to light. Materials such as clay, lithopones or titanium pigments in finely divided form are quite suitable for the purpose. The pigment is preferably applied by first dispersing it in a volatile medium and then coating the sample the scale, we have a paper which is so low in greaseproof propertythatit is not entitled to be marketed as a greaseproof paper. I

Having arranged these various samples in the order of their greaseproof properties, each sample is then subjected to a standard procedure by way of test, and the record of such test'in the form on one side by means of any known method such as by brushing, spraying, doctoring, printing or otherwise. Also, .it is desirable to use such pre-' cautions as to insure that. the particles of pigment are of a certain standard size,.and that the finished dry coating contains a definite amount of pigment per unit of area. It is also desirable that the liquid vehicle should be of such character as of the tested sample is preserved as a standard not to penetrate into the body of the sheetltoo. far

and'also must be capable of being substantially completely evaporated so that its presence will not'aile'ct the test.

The actual testing of the sample consists in applying to the uncoated side of the sample a standard liquid or other material which either contains an oily constituent or is capable of mixing freely with grease or oil. Preferably a uniform standard amount of such material or liquid is applied per unit area of the sheet, and preferably the material is colored or is of a color which will contrast with the color of the pigment coating on the opposite side of the sheet. It is manifest that if any of this oily material penetrates through the sheet, it will be absorbed into the.

pigment coating which will thus exhibit a stain at the point of penetration. According to known standards, the number and size of the stains per unit of area of the sample provide an accurate measure of the greaseproof properties of the test sample.

In the drawing which illustrates a preferred embodiment of the invention;

Fig. l is a plan view of a sample of .paper to be tested, which has been subjected to the prescribed treatment;

Fig. 2 is a section taken on the line 2-2 of Fig. 1; and

Fig. 3 is a plan view of a series of four standard samples with which the test sample is to be compared.

Specific example 'brush, we coat a sample with a liquid which 'consists of titanium dioxide dispersed inmethanol, ethanol or other quick drying medium of a non-aqueous type. No binder of any kind should be used with the .pigment. It is an advantage to grind the pigment in the vehicle, so

that the particles of pigment may be properly suspended in the vehicle and of uniformly small s ze.

After coating the back of the sheet in a uniform manner, the sample is allowed to dry completely before it is subjected to the oil test.

The consistency of the liquid should be adjusted so that the dried coating will contain 15 to 25 grams of dry pigment per square metre, with an optimum of 20 grams of dry pigment per square metre.

The oil test is accomplished by completely covering the uncoated surface of the sample with a fairly penetrating oil or oil solvent, preferably turpentine, with which there has been incorporated suflicient dye, preferably red, so as to contrast well with the white color of the titanium dioxide pigment coating. Said dyed turpentine is applied to the sheet in an amount more than sufiicient to cover the sheet. If the sheet is of the highest greaseproof value. none of the turpentine will penetrate through the sheet, and therefore there will be no red markings visible in the pigmentcoating. However, if the greaseproof properties of the sample are quite low,

the turpentine will rapidly penetrate the sheet at various points, and such penetration will be manifested by the presence of red spots of various sizes and numbers in the titanium coating, visible, of course, upon the exterior of the pigment coating. The number and size of these spots constitute an extremely accurate index of the greaseproof character of the paper which has been subjected to the test treatment.

The details of the procedure above described can, of course, be varied to suit any desired conditions which are encountered or are to be established. The scope of the invention should be determined by reference to the claims.

We claim:

1. The method of evaluating the resistance of a sheet of paper to penetration by grease or oil, which consists in coating one side of a test sam-- ple of the sheet with a pigment, applying to the other side of the sheet a liquid which is miscible with oil and is of such character that when the coating is impregnated with said liquid the appearance of said impregnated coating will contrast with the appearance of the coating which has not been so impregnated, and then comparing the-appearance of the test sample with the appearance of a standard which has been subjected to a similar treatment.

2. The method of evaluating the resistance of a sheet of paper to penetration by grease or oil, which consists in coating one side of a test sample of the sheet with a pigment, applying to the other side of the sheet a liquid which is miscible with oil and is of a color which will contrast with the color of the pigment, and then comparing the appearance of the test sample with the appearance of a standard sample which has been subjected to a similar treatment.

3. The method of evaluating the resistance of a sheet of paper to penetration by grease or oil, which consists in coating one side of a test sample of the sheet with a pigment suspended in a liquid vehicle which, when applied to the sheet, will be retained substantially on the surface of the sheet, evaporating the vehicle so as to leave the pigment coating in dry condition on the said side of the sample, applying to the other side of the sheet a liquid which is misciblewith oil andis of a color which will contrast with the color of the pigment, and then, after a predetermined interval of time, comparing the appear- 7 ance of the test sample with the appearance of a standard sample which has been subjected to a similar treatment.

MILTON G. SCHMITT. MARTIN L. DOWNS. 

